The major aim of this proposal, during the period of requested support, is to determine what effect, if any, bacteriophages have on oral streptococci. Towards this end a search will be made for bacteriophages of oral streptococci resembling S. mutans and a survey made of the frequency with which lysogeny occurs in oral streptococci. It is also intended to determine whether bacteriophages from group A, C, and G streptococci can adsorb, lyse, or lysogenize S. mutans. Experiments are further described which will determine whether bacteriophages are involved in the production of extracellular products by lysogens of S. mutans. Such a phage-host relationship may have a significant role in the production of extracellular products involved in the formation of dental plaque and caries. Finally, it is intended to establish a genetic approach to the study of S. mutans by attempting to transfer genetic markers via transduction and/or transformation.